The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated methyl bromide [ 74‐83‐9], considering all toxicological endpoints. Available publications and unpublished study reports are described in detail. Methyl bromide is a neurotoxin and an irritant to the upper respiratory tract. A NOAEC of 3 ml/m3 for effects in the olfactory epithelium was obtained from the 29‐month inhalation study in the rat, for irritation, the most sensitive endpoint. Based on this, the maximum concentration at the work place (MAK value) for methyl bromide is set at 1 ml/m3(3.9 mg/m3). Since the critical effect of methyl bromide is local, Peak Limitation Category I is designated. In rats, signs of irritation are observed only at methyl bromide concentrations of 20 ml/m3 and above, so an excursion factor of 2 can be given.
There is an adequate margin between NOAEC/L for developmental toxicity and the MAK value. However, methyl bromide is a neurotoxin and no data on developmental neurotoxicity exists. Therefore, methyl bromide is assigned to Pregnancy Risk Group D.
Methyl bromide is genotoxic in vitro and an alkylating substance in vivo. No increased tumour incidence was observed in inhalation studies in mice and rats. Together with the possible relationship between methyl bromide exposure and increased occurrence of prostate carcinomas in a historical cohort study in humans, methyl bromide is still suspected of being carcinogenic and remains in Carcinogen Category 3B. No clastogenic or aneugenic effects are found in vivo with prolonged inhalation and therefore the substance is not regarded as a germ cell mutagen. Skin contact is expected to lead to relatively minor contribution to systemic toxicity. There are no data on sensitization.
Because methyl bromide can be absorbed through the skin from the gaseous phase at high concentrations when respiratory protection is used, biomonitoring studies are recommended in addition to personal protective measures. The BLW value of 12 mg bromide/l plasma or serum must be observed.